1. Field of the Invention
The present invention relates to an information processing apparatus on which a wireless module is mounted to perform wireless communication, and a clock control method used in the information processing apparatus.
2. Description of the Related Art
In general, to impart a wireless communication function to an information processing apparatus such as a personal computer or portable information device (PDA [Personal Digital Assistant]), a wireless communication card implemented by an IC card or compact flash memory which has a wireless module and complies with the PCMCIA (Personal Computer Memory Card International Association) standard is mounted. The information processing apparatus can be used as a wireless module by connecting a wireless communication device such as a portable telephone or PHS (Personal Handyphone System).
When wireless communication is performed in an information processing apparatus having a wireless unit such as a wireless communication device or wireless module, noise increases at a specific wireless frequency which interferes with the operation clock used in a circuit other than the wireless unit, obstructing wireless communication. Hence, the frequency of the operation clock used in a circuit other than the wireless unit must be so designed as not to interfere with the wireless frequency.
However, it is difficult to design the operation clock of a circuit other than the wireless unit so as not to interfere with the entire wireless band in the information processing apparatus which allows mounting a plurality of wireless modules, a portable telephone, and the like, and executes wireless communication by using a plurality of wireless bands.
Even if the frequency of the operation clock is changed during the operation of the information processing apparatus, a change of simply multiplying or dividing the clock frequency by a constant cannot reduce noise generated when the operation clock used in a circuit other than the wireless unit interferes with the wireless frequency to pose a problem in wireless communication.
A technique of changing the clock during the operation of an apparatus is disclosed in, e.g., Japanese Patent Application No. 11-38885. The technique disclosed in Japanese Patent Application No. 11-38885 is a CPU clock control method of controlling the CPU clock in order to reduce EMI (Electromagnetic Interference) and decreasing the clock stepwise (constant multiplication/division) in accordance with the number of interrupt requests.
In the prior art, it is difficult to design the operation clock used in a circuit other than the wireless unit so as to prevent the operation clock used in such a circuit from interfering with the wireless communication frequency. For example, in the use of the technique disclosed in Japanese Patent Application No. 11-38885, even if the operation clock is changed during the operation of the apparatus, a change using constant multiplication/division cannot reduce noise generated when the operation clock used in a circuit other than the wireless unit interferes with the wireless frequency to pose a problem in wireless communication.